Color video images can be displayed on cathode ray tubes with three electron guns, one for each color, and a shadow mask which ensures that electrons from each gun hit only phosphor dots whose color primary matches that intended. The three electron beams are scanned simultaneously. The color primaries in video cameras are also recorded simultaneously so that the camera matches the display.
The simultaneous recording of color primaries at each pixel is now the standard which other display technologies must utilize to retain compatibility with existing infrastructure. An efficient way to get color on a liquid crystal display would be to illuminate it with red, then green, then blue light in turn, but this departs from the convention of simultaneous color primaries. The result is that as an eye follows a moving image, the eye sees the image separate spatially into three parts, each comprising one of the color primaries.
Color separation is avoided by illuminating liquid crystal panels with white light and providing a color filter, one for each primary, over three liquid crystal cells which combine to form a pixel. The color filters are expensive and they waste two thirds of the illumination.
Light emitting diodes have recently become sufficiently bright to illuminate liquid crystal panels economically, but many light emitting diodes must be spaced evenly behind the display if illumination is to be sufficiently uniform. Costs diminish with component count and a few bright light emitting diodes suffice if placed at the end of an acrylic wedge-shaped light-guide which evenly distributes the light across the liquid crystal panel. However, the losses of acrylic are such as to eliminate the advantage otherwise gained by this approach.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known systems.